1. Field of the Invention
This application claims the priority of European Patent Application no. EP 96201503.8 filed May 30, 1996 and U.S. Provisional Patent Application No. 60/025,121 filed on Aug. 30, 1996.
The present invention relates to a semiconductor device including a semiconductor acceleration sensor that converts a displacement into an electric signal using a piezoresistance effect of semiconductor crystal such as silicon, and more particularly to a field in which two-dimensional acceleration is obtained from one structural substance.
2. Description of the Related Art
FIG. 2 is a diagram showing a semiconductor acceleration sensor formed by micro-machining disclosed in Japanese Patent Unexamined Publication No. Hei 1-302167, in which a groove portion 23 is defined in the vicinity of a support of a cantilever by etching to provide a thin portion. A diffused resistor exists on a top surface of the sensor to constitute a bridge circuit. This structural substance is designed to detect one-dimensional acceleration.
Also, in the structures disclosed in Japanese Patent Unexamined Publication No. Sho 63-118667 shown in FIG. 3 and Japanese Patent Unexamined Publication No. Hei 3-202778 shown in FIG. 4, there is provided a structural substance that detects three-dimensional acceleration.
In the conventional semiconductor acceleration sensor, as shown in FIG. 2, a pair of diffused resistors 2 for detecting acceleration constitute a bridge circuit on the surface of the sensor. The acceleration sensor is designed to use the piezoresistance effect, thereby utilizing a phenomenon that a resistivity is changed according to a stress. In the case of detecting acceleration in two-axial or three-axial directions using the above structural substance, there is required the provision of at least two acceleration sensors in detectable directions. Also, in the case of fabricating the structural substances shown in FIGS. 3 and 4, there is required a technique of fabricating a three-dimensional structural substance, such as an etching technique. The above technique suffers from difficulties for high costs in producing the sensor.